Scientists Track Space Junk Using Earthquake Sensors

When a 1.5-ton Chinese space module fell from orbit over California in April 2024, scientists realized something amazing: earthquake sensors had been quietly tracking it the whole way down.

Benjamin Fernando, a researcher at Johns Hopkins University, had a hunch that the sonic booms from the falling debris would show up on southern California's dense network of seismometers. He was right. More than 120 monitoring stations caught the signal.

Working with colleague Constantinos Charalambous from Imperial College London, Fernando analyzed the data and reconstructed the entire descent path. They calculated the module's speed, angle, and trajectory, even mapping how it broke apart as it fell. The results published today in Science reveal a powerful new tool for tracking dangerous space debris.

The timing couldn't be better. Space launches are skyrocketing, and so is the amount of junk falling back to Earth. Most debris burns up completely, but larger pieces pose real risks. The Chinese module passed over major cities on six continents before breaking apart over southern California. U.S. Space Command predicted it would land in the North Atlantic but missed by thousands of kilometers.

The breakthrough works day or night, unlike optical telescopes that only function after dark. Best of all, the seismic networks already exist to monitor earthquakes, so scientists get this tracking capability almost for free once the analysis is automated.

The method could work in near real time, pinpointing crash sites within minutes or even seconds. That's crucial for finding hazardous debris on the ground, especially pieces containing radioactive materials or toxic rocket fuel. Last year, SpaceX Starship debris scattered across the Caribbean, forcing planes to take emergency evasive action.

The Ripple Effect

This discovery extends far beyond finding falling spacecraft. Scientists are increasingly worried about vaporized aerospace materials building up in the upper atmosphere, potentially damaging Earth's protective ozone layer. Better tracking means better understanding of these atmospheric impacts.

The technique could also revolutionize spacecraft design. By studying how objects break apart during reentry, engineers can design future spacecraft to disintegrate more completely, reducing the debris that reaches the ground.

Jonathan McDowell, an astrophysicist at Harvard who tracks spaceflight, calls it "a very useful extra tool in our toolbox." As space activity continues to grow, tools like this become essential for keeping everyone safe.

For 60 years, we've relied on luck that falling space junk wouldn't hit anyone, but this breakthrough means we no longer have to hope for the best when we can track and prepare for what's coming down.